The present invention relates to a vehicle with a turbocharged engine.
Conventionally, turbochargers have been provided to vehicles in order to increase an engine output.
The turbocharger is comprised of a turbine provided to an exhaust passage, a compressor provided to an intake passage, and a coupling shaft coupling the turbine to the compressor, and is configured to transmit rotation of the turbine to the compressor via the coupling shaft. The coupling shaft rotates at a high speed while receiving heat from the turbine through which hot exhaust gas passes, and thus it is necessary to fully cool the coupling shaft and bearings that support the coupling shaft.
JP5494294B2 discloses a vehicle with a turbocharged engine, where engine coolant is supplied into a casing which accommodates a coupling shaft of a turbocharger. The casing that accommodates the coupling shaft communicates with a water jacket formed in an engine body, and the engine coolant cooled by a radiator is supplied into the casing via the water jacket. The casing also communicates with an upper tank of the radiator, and the engine coolant after it cooled bearings which support the coupling shaft flows into the upper tank, and then flows back to the radiator.
Since the engine coolant is boiled at a relatively low temperature near 100° C., the structure in which the turbocharger is cooled by the engine coolant as disclosed in JP5494294B2 may generate steam inside the casing where the engine coolant is supplied, soon after the engine is stopped after a turbocharged operation. When the steam accumulates inside the casing, this makes an introduction of fresh engine coolant difficult and the bearings of the coupling shaft may not be fully cooled. If the steam is to be discharged from the casing in the vehicle disclosed in JP5494294B2, the height of the vertical center of the casing, i.e., the height of the axial center of the coupling shaft, must be located below an upper end of the upper tank of the radiator. Thus, even if a water pump that forcibly circulates the engine coolant is stopped in response to the engine stop, the hot engine coolant and the steam move upwardly by free convection, and are then discharged from the upper tank of the radiator, while cold coolant flows into the space around the bearings to prevent the bearings from seizing (galling). However, the space below the turbocharger becomes smaller around the engine body, resulting in a lesser degree of freedom in the engine layout.